Shallow Saturation Diving on the Alvheim Field

1
Shallow Saturation Diving on the Alvheim Field
An Assessment

• R W K (Bob) Gardiner
• Marathon Petroleum Company (Norway)

2
The Project

• Alvheim Field Development

3
(No Transcript)
4
(No Transcript)
5
Alvheim STP Buoy

• Diving operations on the submerged turret
  production buoy (STP) in preparation for the buoy
  to be pulled into the FPSO when it arrives.
• The water depth varied between 18 and 32 metres.
• The diving operations were conducted from the DSV
  CSO Wellservicer.
• A divers work platform was fabricated onshore to
  underside of STP buoy for ergonomic reasons.

6
(No Transcript)
7
Work on STP Buoy

• Dynamic umbilical hang-off
• Flexible riser hang-off
• STP Buoy installed with 12 mooring lines
• 9 risers 3 umbilicals hung off outer face of
  STP buoy
• Install rotational pull-in frame (c/w winch
  system) to top of STP buoy
• Run pulling wire through I-tubes and cross-haul
  risers/umbilicals to respective hang-off points
• Attach bend stiffeners to corresponding I-tube
  flanged connections on underside of STP buoy
• Secure risers/umbilicals with permanent hang-off
  collars on top of I-tube
• Remove umbilical protection cans and
  laydown/secure umbilical tails
• De-rig worksite and prepare top of STP buoy for
  pull-in to FPSO

8
Shallow Sat Below STP Buoy

• Ergonomics major factor.
• Stage designed to provide divers with place to
  work from.
• Work platform/tool box in centre of stage proved
  very useful.
• Padeyes and lift points positioned all round the
  work area.
• Each riser had its own characteristics during
  pull in. Aforementioned padeyes helped
  considerably.
• Stab jackets used to aid stability and to help
  with equipment transfer.
• Tools sent down with picker and tool box hung off
  underside of the STP buoy for divers.

9
(No Transcript)
10
(No Transcript)
11
Shallow Sat Top of STP Buoy

• Much discussion during planning - surface
  orientated or saturation diving.
• Narrow range in excursion tables.
• Bell could be positioned close to buoy as this is
  considered open-water work. With a more
  traditional platform/ jacket it would be more
  difficult  to access the worksite,
  requiring extended umbilical methodology.
• Diver buoyancy jackets (Stab) used. Divers
  controlled buoyancy before leaving guide weight.
• Facility to control buoyancy (i.e. buoy water
  depth) when working on top of STP buoy.

12
Alvheim STP Buoy
13
Shallow Sat Top of STP Buoy

• Reel for swim line placed on guide weights.
• ROV hook at end of line. This is lowered by diver
  beneath bell.
• ROV takes swim line over to worksite and hooks it
  on to strong point on STP buoy.
• Diver 1 pulls it tight.
• Diver 2 locks out to help with umbilical
  management.
• Diver 1 makes transit along swimline.
• Diver 2 uses swimline or Diver 1s umbilical to
  pull himself over.

14
Shallow Sat Top of STP Buoy

• Cherry picker used to send down equipment.
• Can be sent direct to specific work place so
  divers dont have to leave STP buoy.
• Downline from surface can be attached if picker
  cant be used.

15
(No Transcript)
16
Marine

• Thorough preparation required.
• Experienced DPOs necessary.
• Most marine is worked in 2D. DPOs need 3D.
• Awareness of subsea geometry.
• Awareness of where beacons and tautwire are.
• Where shadows are possible.
• Wellservicer worked with GPS and beacons with
  tautwire as backup.
• Still described as a standard job by skipper.

17
Sum Up

• Saturation is a satisfactory method of work as
  summed up below
• Less personnel exposed to risk more controlled
  operation
• More efficient use of time and resources
• Minimising stress on personnel - both divers and
  surface
• Conclusion - Technically efficient
• Narrow excursion band was a limiting factor.
• What have more recent studies, performed after
  the generation of current excursion tables,
  concluded?
• Does the industry need to review the basis for
  the current excursion limits?

18
Shallow Saturation Diving on the Alvheim Field
An Assessment

• R W K (Bob) Gardiner
• Marathon Petroleum Company (Norway)